Motor fuels containing monocarboxylic acids



United States Patent Office 3,541,723 Patented Nov. 24, 1970 Int. Cl. CllOl US. Cl. 4466 6 Claims This invention relates to a hydrocarbon fuel composition of high octane rating. More specifically, it involves the discovery that the octane rating of leaded gasoline fuels is substantially improved by the addition of carboxylic acids.

The recent increases in compression ratios of automobile engines have placed a severe strain on petroleum refiners to produce fuels having the octane rating demanded by these engines. Premium fuels at the present time have research octane ratings between 97 and 100 and it has been predicted that premium fuels will have to have octane ratings between 105 and 110 five years from now in order to satisfy the octane requirements of the high compression automative engines predicted for that date. In order to produce premium fuels of octane ratings of 97 and above, it has been necesary for refiners to rely heavily on catalytic refining operations such as fluid catalytic cracking, catalytic reforming, alkylation and catalytic isomeration.

Catalytic cracking and catalytic reforming, which are the most Widely used refining operations in the production of high octane fuels, produce substantial quantities of aromatics; catalytic cracking also produces a substantial amount of olefins. It is well-known that ole-fins and aromatics, although possessing high octane ratings, have a poorer response to organo-lead compounds such as tetraethyl lead than saturated aliphatic gasoline components. Accordingly, as the aromatic and olefinic content of the gasolines have increased to meet the octane levels required by modern automotive high compression engines, the lead response of the resulting fuels has diminished. Stated another way, the octane increment obtainable by the addition of an organo-lead compound decreases as the aromatic and olefin contents of the base fuel increase. The subject invention involves the discovery that the octane rating of leaded motor fuels containing a substantial concentration of high octane components, that is, aromatics, olefins and mixtures thereof, is markedly improved by the addition of a small amount of a monocarboxylic acid.

The high octane hydrocarbon motor fuel of this invention comprises high octane components including a substantial concentration of aromatic hydrocarbons, olefinic hydrocarbons or mixtures thereof, an organo-lead antiknock agent, and a monocarboxylic acid in a concentration of at least 0.1 volume percent of the fuel.

The action of monocarboxylic acids in raising the octane rating of gasoline is characterized by several unusual features. In the first instance, the carboxylic acids appear to be ineffective in raising the octane rating of gasolines unless an organo-lead anti-knock agent, normally tetraethyl lead, is a component of the gasoline mixture.

The second unusual characteristic of the action of monocarboxylic acids in appreciating the octane rating of gasolines is the fact that equal concentrations of acids appear to cause a greater octane improvement above the 100 octane level than below the 100 octane level. For example, a 3.9 unit octane improvement on the research scale has been realized with 0.5 weight percent concentration of Z-ethylhexanoic acid in 105 octane base fuel,

whereas only a 2.3 unit improvement was realized with the same concentration of 2-ethylhexanoic acid in a base fuel having a 96.6 octane rating.

The third unusual feature of the action of monocarboxylic acids is that they appear to have substantially no effect on the octane rating of a gasoline consisting essentially of saturated aliphatic hydrocarbons even though an organo-lead anti-knock agent is present. Since organolead anti-knock agents exert their greatest octane appreciation in predominantly saturated paraflinic base hydrocarbon gasolines and have the least effect on the octane rating of aromatic and olefin rich gasolines, the present invention neatly complements tetraethyl lead as an octane improver. Monocarboxylic acids have their minimum effect where tetraethyl lead has its maximum effect and exert their maximum effect on octane values where tetraethyl lead has its minimum effect.

The novel fuel compositions of this invention have a minimum concentration of aromatic and/or olefin components of at least 10 volume percent. The aromatic and/or olefin components of the motor fuel of the invention can constitute as high as volume percent thereof but usually fall between 20 and 20 volume percent. The minimum 10 percent concentration is necessary for monocarboxylic acids to exert a significant octane improvement.

The aromatic components of the motor fuel of the invention are generally supplied by catalytic reforming or catalytic cracking operations. Catalytic reformate is particularly high in aromatics. The olefin components of the motor fuel of the invention are derived either from thermal cracking, catalytic cracking or polymerization.

The organo-lead reagent necessary for the action of monocarboxylic acids as octane improvers is a tetraalkyl lead compound of the class known to possess anti knock action. Tetraethyl lead is practically universally used as an anti-knock agent but other tetraalkyl lead compounds such as tetramethyl lead, tetrabutyl lead, tetraamyl lead, tetrapropyl lead, etc. are known to possess antiknock properties and may be used in the fuel compositions of the invention in conjunction with monocarboxylic acids.

The tetraethyl lead mixtures commercially available for automotive use contain an ethylene chloride-ethylene bromide mixture as a scavenger for removing lead from the combustion chamber in the form of volatile lead halides. As is used hereafter in the examples illustrating the invention, tetraethyl lead fluid denotes the commercial product which comprises tetraethyl lead, ethylene chloride and ethylene bromide, the latter two reagents being present in 1.0 theory and 0.5 theory respectively, theory denoting the stoichiometric amount required for reaction with the lead content of the tetraethyl lead.

The organo-lead reagent is present in the fuel compositions of the invention in concentrations between 0.5 ml. per gallon up to the statutory limit of organo-lead reagent concentration which, at the present time, is 3 ml. per gallon in the case of automotive fuel and 4.6 ml. per gallon in the case of aviation fuel. The usual concentration of tetraethyl lead is between 1 and 3 ml. per gallon in automotive gasoline and 2-4.'6 ml. per gallon in aviation gasoline.

Monocarboxylic acids which are eflzective in increasing the octane rating of an aromatic and/ or olefin-containing gasoline in the presence of an organo-lead anti-knock agent, contain 1 to 30 carbon atoms and have the general formula: RCOOH wherein R is hydrogen or a hydro- .carbyl radical containing 1 to 29 carbon atoms. Aliphatic monocarboxylic acids, cycloaliphatic monocarboxylic acids, and aromatic monocarboxylic acids have all been found to be octane appreciators in leaded fuels containing a substantial aromatic and/or olefin content. Apparently, the action is a function of the carboxylic acid radical since aliphatic acids from formic acid up to and including behenic acid, aryl acids such as benzoic acid and cumic acid and cycloaliphatic acids have been effective in raising the octane rating of the fuel compositions of the invention.

As will be evident from the following list of monocarboxylic acids that are eifective as octane apreciators in the fuel compositions of the invention, the radical attached to the carboxylic acid radical in the general formula RCOOH can be hydrogen, a saturated hydrocarbon radical, an unsaturated hydrocarbon radical, an aryl radical, an alkaryl radical, an aralkyl radical, or a cycloalkyI radical. Monocarboxylic acids that have been effective in the fuel compositions of the invention as octane improvers are the following:

Acetic acid, formic acid, propionic acid, caproic acid, n-heptanoic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, 2- ethylbutyric acid, 4-methylvaleric acid, 2-ethylhexanoic acid, cumic acid, benzoic acid, cyclohexane carboxylic acid, cinnamic acid, phenylacetic acid, oleic acid, Snodotte acids (hydrogenated fish oil fatty acids comprising mainly C to C acids), and coconut fatty acids (comprising mainly a mixture of C to C fatty acids).

Although monocarboxylic acids containing 1 to 30 carbon atoms are effective in the fuel compositions of the invention, the preferred acids contain 6 to 14 carbon atoms and are either aliphatic monocarboxylic acids or aromatic monocarboxylic acids. Monocarboxylic acids containing less than 6 carbon atoms are effective as octane irnprovers but have the serious drawbacks of being water-soluble, odoriferous and corrosive to metals. Preferred acids are Z-ethylhexanoic, benzoic, caprylic, capric, lauric, and myristic.

Hydroxy monocarboxylic acids such as salicylic and ricinoleic acid, halogenated carboxylic acids such as alphachloro-propionic acid and sulfhydryl-su-bstituted carboxylic acids such as mercapto-acetic acid, are ineffective in raising the octane rating of leaded fuels containing a substantial content of aromatics and olefins. Amino acids are too insoluble in gasoline hydrocarbons to be effective as actane appreciators. The ineffectiveness of the substitued hydrocarbon monocarboxylic acids of the types mentioned is another surprising feature of this invention.

The monocarboxylic acids must be present in the leaded aromatic and/ or olefin-containing compositions of the invention in a minimum concentration of 0.1 volume percent before a significant octane appreciation is realized. With monocarboxylic acid concentrations below 0.1 volume percent, no octane improvement is obtained in leaded gasoline containing at least 10 volume percent aromatics and/ or olefins. The preferred concentration of monocarboxylic acid in the fuel compositions of the invention falls between 0.2 and 1.0 volume percent with maximum octane appreciation generally being obtained at a concentration level of about 0.5 volume percent. Concentrations of monocarboxylic acids as high as 5 volume percent can be incorporated in the fuel compositions but no additional octane improvement is realized at the higher concentrations and economic considerations preclude the use of such concentrations in commecrial fuel compositions.

In Table I there is shown the action of monocarboxylic acids in raising the octane rating of the leaded fuel compositions of the invention. The base gasoline to which the various acids were added in the indicated concentrations was a catalytically reformed naphtha containing 3 cc. of tetraethyl lead fluid per gallon and having an IBP of 130 F. and an end point of 394 F. The base fuel had a leaded research octane rating of 96.6 and an aromatic concentration of 48 volume percent as measured by Fluorescent Indicator Analysis (FIA) Method.

,/ TABLE I Research octane numbers in 96.6 base fuel Percent Acid O. 05 0.1 0.25 0.50 0.75

2-ethyl butyric 4mcthyl Valerie 2 ethyl hexanoic 96. 6 98. 5 C10 acid obatined by oxidation of prodnot of carbonylation of propylene tnmer Di-neopentyl acetic Neopentyl, t-butyl methyl ac Oleic Coconut fatty acids. Snodotte acids Cyclohexane cax'boxylic-- Phenyl acetic Cinnamic Benzoic 99. 0

The data in the foregoing table demonstrate very clearly the effectiveness of the prescribed concentrations of hydrocarbon monocarboxylic acids in raising the octane rating of leaded gasoline having the prescribed aromatic content. The wide scope of the action of the acids is particularly significant with substantial improvement in octane rating being obtained with monocarboxylic acids containing 1-22 carbon atoms.

The data in Table I also demonstrate the necessity of employing a concentration of at least 0.1 volume percent in order to obtain any measurable octane appreciation of the leaded fuel. The addition of 0.05 volume percent of 2-ethy1 hexanoic acid, one of the most effective acids, had no measurable effect on the octane rating of the base fuel, whereas almost a two unit improvement was obtained at a concentration of 0.1 volume percent of the same acid.

In Table II there is shown the action of various acids in improving the octane rating of a leaded gasoline having an octane rating of 100. The base fuel employed in Table II was a blend comprising approximately 5 percent butane, 38 percent light fluid catalytically cracked naphtha, and 57 percent catalytically reformed naphtha. The base fuel contained 3 cc. of tetraethyl lead fluid per gallon and had an aromatic content of approximately 24 volume percent as measured by FIA Method. The 100 octane base fuel had an IBP of 98 F. and an end point of 363 F.

TABLE II Research octane values in 100 octane gasoline Volume percent of acid in fuel 0. 1 0. 25 0.50 1. 00 2. 00

Acids:

Laurie 99. 9 100. 1 100. 4 101. 8 100. 9

Capric 99. 4 99. 6 100.5 101.

N eopentyl, t-butyl, methyl acetic 99. 9 100. 4 100.9 Cumic 9 100.7 Oyclohexane carbox 1c. 10

2-ethylhexanoic Benzoie 1 0.2 percent.

TABLE III TABLE V Research octane values-- Research octane 105 octane gasoline umber Volume percent of acid 0.1 0.25 0.50 1.00 With3 A 5 ccJgal. Acids: l Clear TEL. fluid.

Cyclohexane carboxylic 105.8 106.5 107.8 106.7 2-ethylhexanoic 107.6 109.2 Base fuel D- 84.3 97.8 Benzoic 106.0 107.9 108.6 107.4 0 percent 2-ethylhexanoie d 84.3 98.1 Base fuel 1].. 69.2 86.9 Basefuel E plus 0.5 vol. percent itethylhexanoic 0 acid 69.7 86.8 The octane improvements in the 105' octane base fuel resulting from-the addition of the 0.1 to 1.0 volume percent acid are dramatic. The 3.9 unit improvement in The data in Table v Show that in Predominantly wresearch octane Value obtalnefi yf adfiltlon P rated aliphatic gasoline, the addition of the hydrocarbon Volume Percent z-ethylhexanolc acld, the 2 monocarboxylic acid has substantially no effect on the P P F fesllltlng from f q Same concentratlor} of octane rating of the fuel even in the presence of the or- 1010 acld, and the unitimprovengwm'resultme e gano-lead anti-knock agent. It is noteworthy that it is in the p fl same' cqncemr'fltlon f q f such fuels that tetraethyl lead is particularly effective in carboxylic acid are outstanding. Prior to this mvention, increasing h octane rating octane improvements of this magnitude at the 105. octane In Table VI ii Shown that both the research and leflel were consldel'ed lmPQ t0 atta1I1- I 15 gmotor octane ratings of a commercial gasoline containing nlfiifant .ih greater Pctane I P obtalned y 3 cc. of tetraethyl lead fluid per gallon, and comprising q Y l concentratloll? P 0 1 -fi y h x approximately 26 percent aromatic hydrocarbons, 14 pern cyclohexane cal'boxyllc i 111 tal1eba$e 2r cent olefins and '60 percent saturated hydrocarbons are fuel than in the 96.6 and 100 octane base fuels of Tables Iand II,respectively. f

. significantly improved by the addition of the prescribed amounts of Z-ethylhexanoic acid and benzoic acid.

TABLE VI I Base fuel plus 0.2 vol. percent benzoic acid In Table IV there the necessity of an qrganolead anti-knock agent in the aromatic and/ or olefincontaining fuel in order for themonocarboxylic acid to effect octane improvement of the fuel. Base Fuel A em;

ployed in Table IV was the catalytically reformed naphtha employed in Table I. f

TABLE IV Research octane numbers With 3 ccJgal. Clear TEL. fluid Base fuel A 87. 7 96. 7 Base fuel A plus 0.5 vol. percent 2-ethylhexanoic acid 87. 4 98. 9 Base fuel A plus 0.5 vol. percent benzoic acid 88.0 98. 5 Pentene-2 95. 1 98. 6 Pentene-2 plus 0.5 vol. percent benzoic acid. 94. 6 99. 4 Heavy C.R. Naphtha 103. 4 105. 6 Heavy C.R. Naphtha plus 0.5 vol. percent benzoic acid- 2. 9 108. 0

In Table VII there is compared the action of monocarboxylic acids on the octane ratings of three different blends of high octane gasoline components. The aromatic gasoline blend had a boiling point range of 228 to 378 F. and comprised 84I percent aromatics, 15 percent saturated aliphatic hydrocarbons and 1 percent olefinic hydrocarbons. Olefinic gasoline blend A consists essentially of a mixture of dimers and trimers of propylene having a boiling point range of 102430 F. Olefinic gasoline blend B comprised 50 percent isooctene and 50 percent isoheptene. The isoparafiinic gasoline blend comprised 10 percent isopentane, 5 percent n-heptane and 85 percent isooctane.

Table VII Research octane numbers with 3 cc./ gal. TEL. fluid Aromatic gasoline 108.3 Aromatic Gasoline+0.5 vol. percent benzoic acid 110.6 Aromatic gasoline+0.5 vol. percent 2 ethylhex- Isoparaflinic gasoline blend+0.5 vol. percent 2- ethylhexanoic acid 105.1

The data in Table VII demonstrate clearly the effectiveness of monocarboxylic'acids in raising the octane ratings of leaded aromatic and olefinic gasolines and the ineffectiveness of the same acids in improving the octane ratings of a leaded isoparafiinic gasoline. These data indicate clearly that the gasoline blend must have an aromatic and/ or olefin content above about volume percent in order for the monocarboxylic acids to act as octane improvers.

In Table VIII, data are presented to show the ineifec tiveness of hydroxy monocarboxylic acids, halo-substituted monocarboxylic acids, and mercapto-substituted monocarboxylic acids in raising the octane rating of leaded gasoline. The base fuel employed in Table VHI was the catalytically reformed naphtha described in connection with the data presented in Table I. This base fuel had an aromatic concentration of 48 volume percent and contained 3 cc. of tetraethyl lead fluid per gallon.

In addition to the hydrocarbon monocarboxylic acids, halo-monocarboxylic acids and mercapto-monocarboxylic acids shown to be ineffective in Table VIII, amino acids are unable to exert any positive action in raising the octane rating of leaded fuels containing the requisite aromatic and/or olefin content because of their insolubility in gasoline hydrocarbons.

Obviously, many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof and, therefore, only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. A hydrocarbon fuel in the gasoline boiling range containing an organo-lead anti-knock agent, high octane components selected from the group consisting of olefinic hydrocarbons, aromatic hydrocarbons and mixtures thereof in a concentration of at least about 10 volume percent of said fuel and an aromatic monocarboxylic acid containing up to 30 carbon atoms in a concentration between 0.1 and 5.0 volume percent, said amount being sufiicient to effect substantial improvement of the octane rating of said organo-lead-containing hydrocarbon fuel.

2. A hydrocarbon fuel according to claim 1 in which said aromatic monocarboxylic acid is a benzene monocarboxylic acid.

3. A hydrocarbon fuel according to claim 1 in which said aromatic monocarboxylic acid is benzoic acid.

4. A hydrocarbon fuel according to claim 1 in which said aromatic monocarboxylic acid is phenylacetic acid.

5. A hydrocarbon fuel according to claim 1 in which said aromatic monocarboxylic acid is cinnamic acid.

6. A hydrocarbon fuel composition according to claim 1 in which said aromatic monocarboxylic acid is cumic acid.

References Cited UNITED STATES PATENTS 2,125,448 8/1938 Johnson 44-66 X 2,667,408 1/ 1954 Kleinholz 4466 X 1,692,784 11/ 1928 Orelup 44-66 2,426,709 9/ 1947 Roddy 44-66 X 2,360,585 10/1944 Ross et al. 44-80 FOREIGN PATENTS 277,326 1/ 1929 Great Britain.

599,222 3 1948 Great Britain.

640,311 7/ 1928 France.

OTHER REFERENCES Improved Motor Fuels Through Selective Blending, Wagner et al., Paper Presented Before American Petroleum Institute Nov. 7, 1941.

Aviation Gasoline Manufacture, by Van Winkle, lggiGraw-Hill Book Co. Inc., 1944, 1st edition, pp. 199- PATRICK P. GARVIN, Primary Examiner Y. H. SMITH, Assistant Examiner US. 01. X.R. 4469 

1. A HYDROCARBON FUEL IN THE GASOLINE BOILING RANGE CONTAINING AN ORGANO-LEAD ANTI-KNOCK AGENT, HIGH OCTANE COMPONENTS SELECTED FROM THE GROUP CONSISTING OF OLEFINIC HYDROCARBONS, AROMATIC HYDROCARBONS AND MIXTURES THEREOF IN A CONCENTRATION OF AT LEAST ABOUT 10 VOLUME PERCENT OF SAID FUEL AND AN AROMATIC MONOCARBOXYLIC ACID CONTAINING UP TO 30 CARBON ATOMS IN A CONCENTRATION BETWEEN 0.1 AND 5.0 VOLUME PERCENT, SAID AMOUNT BEING SUFFICIENT TO EFFECT SUBSTANTIAL IMPROVEMENT OF THE OCTANE RATING OF SAID ORGANO-LEAD-CONTAINING HYDROCARBON FUEL. 